AppttoObs Parameters
CALL sla_AOPPA (DATE, DUT, ELONGM, PHIM, HM, XP, YP,
TDK, PMB, RH, WL, TLR, AOPRMS)
DATE  D  UTC date/time (Modified Julian Date, JD$$2400000.5) 
 
DUT  D  $\Delta $UT: UT1$$UTC (UTC seconds) 
 
ELONGM  D  observer’s mean longitude (radians, east +ve) 
 
PHIM  D  observer’s mean geodetic latitude (radians) 
 
HM  D  observer’s height above sea level (metres) 


XP,YP  D  polar motion $\left[\phantom{\rule{0.3em}{0ex}}x,y\phantom{\rule{0.3em}{0ex}}\right]$ coordinates (radians) 


TDK  D  local ambient temperature (K; std=273.15D0) 


PMB  D  local atmospheric pressure (mb; std=1013.25D0) 


RH  D  local relative humidity (in the range 0D0 – 1D0) 


WL  D  effective wavelength ($\mu m$, e.g. 0.55D0) 


TLR  D  tropospheric lapse rate (K per metre, e.g. 0.0065D0) 
AOPRMS  D(14)  starindependent apparenttoobserved parameters: 
 
(1) 
 geodetic latitude (radians) 
(2,3) 
 sine and cosine of geodetic latitude 
(4) 
 magnitude of diurnal aberration vector 
(5) 
 height (HM) 
(6) 
 ambient temperature (TDK) 
(7) 
 pressure (PMB) 
(8) 
 relative humidity (RH) 
(9) 
 wavelength (WL) 
(10) 
 lapse rate (TLR) 
(11,12) 
 refraction constants A and B (radians) 
(13) 
 longitude + eqn of equinoxes + “sidereal $\Delta $UT” (radians) 
(14) 
 local apparent sidereal time (radians) 
HM=29.3D0*TSL*LOG(P/1013.25D0)
where TSL is the approximate sealevel air temperature in K (see Astrophysical Quantities, C.W.Allen, 3rd edition, §52). Similarly, if the pressure P is not known, it can be estimated from the height of the observing station, HM as follows:
P=1013.25D0*EXP(HM/(29.3D0*TSL))
Note, however, that the refraction is nearly proportional to the pressure and that an accurate P value is important for precise work.